A new study bolstering scientists’ hot new “hygiene theory” shows exposing kids at a very young age to other kids and their germs actually protects the youngsters from developing asthma.

The study found babies who were placed in day care in their first six months – or had two or more older siblings at home – were about half as likely to have asthma by age 13 as kids who went to day care when they were older, or had just one or no older brothers and sisters at home.

The “hygiene theory” suggests that children who don’t get outside and get dirty once in awhile aren’t exposed to enough germs to stimulate their immune systems.

The study, funded by the National Heart, Lung and Blood Institute, appears in the current New England Journal of Medicine.